Process for producing metallic articles by electroslag remelting

ABSTRACT

A method of forming a bath of molten slage for use in the production of metallic articles by an electroslag melting process which method comprises connecting non-consumable electrodes to the lower ends of metallic electrodes to be melted in the electroslag melting process, filling a mould to be used in the electroslag melting process with flux so that the lower ends, at least, of the non-consumable electrodes, are below the level of the flux and passing an electric current between adjacent ones of the non-consumable electrodes, whereby the flux is melted to form the bath of molten slag. Then, the non-consumable electrodes are disconnected from the metallic electrodes and the latter have their lower ends dipped into the molten slag pool and begin to become consumed.

[ Sept. 17, 1974 PROCESS FOR PRODUCING METALLIC ARTICLES BY ELECTROSLAG REMELTING Inventor:

Akira Ujiie, Kobe, Japan Mitsubishi Jukogyo Kabushiki Kaisha, Tokyo, Japan Filed: Feb. 12, 1973 App]. No.: 331,707

Assignee:

[30] Foreign Application Priority Data Mar. 1, 1972 Japan 4720563 [5 6] References Cited UNITED STATES PATENTS Primary ExaminerJ. Spencer Overholser Assistant Examiner-John E. Roethel Attorney, Agent, or FirmCushman, Darby & Cushman 5 7 ABSTRACT A method of forming a bath of molten slage for use in the production of metallic articles by an electroslag melting process which method comprises connecting non-consumable electrodes to the lower ends of metallic electrodes to be melted in the electroslag melting process, filling a mould to be used in the electroslag melting process with flux so that the lower ends, at least, of the non-consumable electrodes, are below the level of the flux and passing an electric current between adjacent ones of the non consumable electrodes, whereby the flux is melted to form the bath of molten slag. Then, the non-consumable electrodes are disconnected from the metallic electrodes and the latter have their lower ends dipped into the molten slag pool and begin to become consumed.

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PAIENTED SEP I 7 I974 SHEEI 2 BF 2 PROCESS FOR PRODUCING METALLIC ARTICLES BY ELECTROSLAG REMELTING FIELD OF THE INVENTION This invention relates to a method of forming a bath of molten slag which is suitable for use in the production of metallic products of desired shapes and dimensions, e.g. in the production of tubular, elbow-shaped or spherical products. It is particularly suitable for use in the formation of large-sized products having large diameters or large wall thicknesses, by re-melting metallic material by electroslag melting and solidifying the molten metals in metal moulds, wherein a large bath of molten slat is required.

BACKGROUND OF THE INVENTION In the past, it has been conventional in Japan to form a bath of molten slag by generating arcs across the tip ends of electrodes and melting a powdered flux by the heat of the arcs, as has been practised in electroslag welding. However, when this method of forming a bath of molten slag is used in the formation of products by electro-slag re-melting, there arises the danger that sparks will pass between the electrodes and a metal mould causing generation of arcs between the electrodes and the metal mould and resulting in damage to the metal mould. There is also the danger that the molten metal formed by the melting of metallic electrode will solidify on and stick fast to the metal mould on being cooled by the metal mould, since the temperature of the slag bath is insufficiently high. Such dangers occur particularly when the desired product is large in transverse cross-sectional area and arcs are generated in a metal mould having a large cross-section. Therefore, the method described above is not suitable for use in the formation of metallic products by electroslag remelting. Hitherto in Japan a method has mainly been employed in which molten slat formed in a separate molten slag forming apparatus is poured into the metal mould. Such a method, however, involves the problem that it requires a large apparatus for forming a large amount of molten slag, particularly for the production of a product having a large cross-section. In addition, the molten slag tends to cool and solidify during the pouring operation which takes a long time.

SUMMARY OF THE INVENTION According to the present invention there is provided a method of forming a bath of molten slag for use in the production of metallic acticles by an electroslag melting process which method comprises connecting nonconsumable electrodes to the lower ends of metallic electrodes to be melted in the electroslag melting process, filling a mould to be used in the electroslag melting process with flux so that the lower ends, at least, of the non-consumable electrodes, are below the level of the flux and passing an electric current between adjacent ones of the non-consumable electrodes, whereby the flux is melted to form the bath of molten slag. Then, the non-consumable electrodes are disconnected from the metallic electrodes and the latter have their lower ends dipped into the molten slag pool and begin to become consumed. The method of the invention is advantageous particularly for the production of metallic articles having large cross-sections. It involves substantially no molten slag waste nor heat loss as compared with the method in wich a molten slat bath is formed by pouring molten slag, formed by a separate apparatus, into a metal mould. Furthermore the provision of a special large molten slag forming apparatus is not required and a moulding operation can be started promtply, even when a large amount of molten slag is required. It is also advantageous in that the danger induced by the occurrence of sparks or damage to the metal mould can be eliminated, as contrasted to the conventional method in which a molten slag bath is formed by melting a powdered flux in a metal mould by metallic electrodes. A further advantage of the method of this invention is that, when the moulding operation is interrupted for any reason (e.g. due to power stoppage), restart of the operation is easy and, since the temperature of the molten slag bath can be elevated to a desired level at the re-start of the operation, the portion of the metal mould where re-melting of the previously solidified metal isstarted, can be sufficiently pre-heated, so that there is no fear of the molten metal thus re-melted and the molten metal formed after re-start of the operation being interfused unsatisfactorily, and consequently a quality product can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further illustrated by reference to the accompanying drawings showing, by way of example, an embodiment of the invention, in which:

FIG. 1 is a side elevational view, partially in section, of one form of apparatus for practising the present invention;

FIG. 2 is an illustrative view showing the manner in which a non-consumable electrode is connected to a metallic electrode; and

FIG. 3 is an illustrative view showing the arrangement of the metallic electrodes and non-consumable electrodes, relative to the metal mould, electrical connections between the metallic electrodes, the nonconsumable electrodes and the start piece, and the source of power.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT As shown in FIG. 1, a relatively shallow pit 2 is formed in a floor 1 and a base block 3 is provided on the floor substantially in the centre of the pit 2. A ring gear 5 having internal threads on its inner surface and gear teeth on its outer surface is rotatably mounted on the base block 3 by means of a bearing 4. Also disposed in the pit 2 is a drive motor 7. A gear 6 is fixedly mounted on the end of the drive shaft of the drive motor 7 and is in meshing engagement with the gear teeth of the ring gear 5. Thus, the ring gear 5 is driven by the drive motor 7 in one or the other direction round its own axis, while being held in its position. A spindle 8 having an external thread on its outer surface extends through the ring gear 5, the external threads meshing with the internal thread of the ring gear 5. The top end of the spindle 8 is fixed to the centre of a bottom plate of an annular bracket 9a which projects above the floor 1 through an annular slit lb formed in a floor plate la. A disc-like table 9 having a central bore 9b is fixed to the upper edge of the annular bracket 9a, horizontally and with the bore 9b in axial alignment with the spindle 8. A start piece 10 consisting of a short tube is fixedly mounted on the table 9 in concentric relation thereto, the transverse sectional shape of the start piece 10 being the same as that of a tubular body desired to be produced. The arrangement of the apparatus is such that when a water-cooled metal mould M, to be described later, is at the lower end of its stroke, the top end of the start piece is received in a central parallel-walled portion of the moulding space of the metal mould M, so that the upper face of start piece 10 closes the moulding space at the boundary between the central parallel-walled portion and an upwardly opening enlarged portion thereabove of the moulding space. Since the start piece 10 is connected to the spindle 8 through the table 9 and annular bracket 9a, as described above, when the drive motor 7 is driven in one or the other direction, the start piece 10 is moved up or down in a vertical direction within the effective stroke of the spindle 8 while rotating in one or the other direction together with the spindle 8. A three-phase AC. power source 11 is provided on the floor 1, with its N pole connected to the start piece 10 through the table 9 and its U, V, W poles connected to nonconsumable electrodes 35 provided one on each metallic electrode 18, as will be described later, through a disc (see FIG. 3). A ceiling plate 12 is provided squarely above the floor plate la and a vertical threaded spindle 24 extends between the centres of the ceiling and floor plates 12 and 1 respectively, in axial alignment with the spindle 8 and rotatably supported by the plates by means of bearings 24a and 24b. The top end of the spindle 24 extends upwardly through the ceiling plate 12 and is connected with the drive shaft of a motor 30 which is mounted on a bracket 12a provided on the upper surface of the ceiling plate 12. A ring-shaped disc 15 has teeth formed on its outer peripheral surface and is rotatably supported by means of a bearing 14 on a bracket 13 which projects downwardly from the lower surface of the ceiling plate 12. This disc 15 provides a supporting member for supporting a plurality of metallic electrodes 18 in their preset positions respectively and is provided on its lower surface with a plurality (six in the embodiment shown) of circumferentially equally spaced fixing means, arranged along a circle of a predetermined diameter, to which the metallic electrodes 18 are fixed at their top ends respectively, each electrode being supported in a vertical position. Each metallic electrode 18 is of such a length that when the water-cooled metal mould M, to be described later, is at the lower end of its stroke, the lower end of each metallic electrode is located at about the centre of the enlarged upwardly opening portion of the moulding space of the metal mould. The arrangement of these metallic electrodes 18 in a horizontal plane, is as shown in FIG. 3.

A motor 16 is mounted on a suitable location on the ceiling plate 12 by means of a bracket 12b. A gear 17 fixedly mounted on the drive shaft of the motor 16 meshes with teeth provided on the outer peripheral surface of the ring-shaped disc 15. The arrangement is such that when the motor 16 is set in motion, the metallic electrodes 18 periodically bodily move around the axis of the disc 15 at an optional speed integrally with the disc 15 in one or the other direction, without moving in a vertical direction. Each of the metallic electrodes 18 is electrically connected through a contact shoe l9 and the disc 15 to the aforesaid AC. power source 11, to be supplied with a current therefrom.

The metal mould M consists of a water-cooled core mould 20 and a watercooled outer mould 21. Both the core and outer moulds 20 and 21 are cooled by water circulating therethrough. The core mould 21 and outer mould 22 define therebetween a moulding space which, in a vertical cross-section, has an enlarged upwardly opening portion in the shape of a hopper, a cylindrical parallel-walled portion and a downwardly expanding conical portion as shown in FIG. 1. The transverse cross-sectional shape of the central parallelwalled portion is the same as that of the metallic product to be produced. The core mould 21 has at the central portion thereof arms 22 each having a nut 23 fixed thereto, which nuts 23 are held in meshing engagement with a vertical threaded spindle 24. Thus, the core mould 20 moves up or down in a vertical direction at a predetermined speed, incident to the rotation of the spindle 24. Elongate worms 25 and 25 extend upright between the floor plate 10 and ceiling plate 12, and are rotatably supported by the floor and ceiling plates by means of bearings 26, 27 and 26, 27 respectively as shown in FIG. 1. The top ends of these elongate worms 25 and 25' project upwardly through the ceiling plate 12, and pulleys 28 and 28' respectively are fixedly mounted on the projecting ends thereof. Pulleys 29 and 29 are fixedly mounted on the upwardly projecting end of the spindle 24, and belts are engaged around the pulleys 28, 29 and 28, 29 respectively. Thus, the elongate worms 25 and 25 are driven simultaneously by the motor 30 by means of these pulleys and belts in one or the other direction, in the same direction of rotation and at the same speed as the spindle 24. The annular outer mould 21 is provided with support arms 31 and 31', having nuts 32 and 32' respectively fixed to the outer ends thereof, and these nuts 32 and 32 are held in meshing engagement with the worms 25 and 25 respectively. Therefore, the outer mould 21 moves up or down incident to the rotation of the worms 25 and 25 in one or the other direction, caused by the motor 30, in synchronism with the movement of the core mould 20. The upright threaded spindle 24, the elongate worms 25, 25 and the motor 30. to drive the spindle and the worms, all together constitute elevating means for moving the metal mould M up or down in a vertical direction at a predetermined speed. Flux supplying hoppers 33 and 33' are respectively supported by support arms, with their bottom openings located above the upwardly opening portion of the moulding space of the metal mould M. The support arms respectively have nuts 34 and 34' threadedly mounted on the worms 25 and 25'. These hoppers 33 and 33 also move up or down incident to the rotation of the worms 25 and 25 in one or the other direction in synchronism with the movement of the metal mould M.

The non-consumable electrodes 35 are removably connected one to the lower end of each metallic electrode 18 by wing nuts 37 through a socket 36 as shown in FIG. 2. These electrodes are, for example, carbon electrodes and respectively electrically connected to the U,V, W poles of the three-phase A. C. power source 11 as shown in FIG. 3. Further, these carbon electrodes 35 are arranged such that adjacent electrodes are spaced from each other by an interval small enough to generate an arc thereacross at the voltage supplied from the power source 11.

Reference numeral 38 designates the powdered flux placed in the upwardly opening portion of the metal mould M. The upwardly opening portion of the metal mould M is filled with the powdered flux 38, the metal mould is elevated to a position in which the nonconsumable electrodes 35 are embedded in the flux and then a current is passed through the nonconsumable electrodes 35, whereby an arc is generated across the adjacent electrodes through the powdered flux 38 and the flux is melted by the heat of the arcs, forming a molten slag bath in the metal mould.

In forming a molten slag bath in the metal mould M by the method of this invention, the non-consumable electrodes (for example carbon electrodes) 35 are connected each to the lower end of each metallic electrode 18 at first and then the metallic electrodes are mounted in the apparatus, upon lowering the metal mould M to the lower end of its stroke, in such a manner that the carbon electrodes 35 are located within the upwardly opening portion of the moulding space of the metal mould. Thereafter, the powdered flux 38 is poured into the upwardly opening portion of the metal mould up to a level at which the carbon electrodes 35 are embedded therein. When the circuit of the three-phase AC. power source 11 is closed and the adjacent carbon electrodes 35 are scratched by a carbon piece not shown, an arc is generated across the carbon electrodes through the powdered flux 38. In this case, since the powdered flux 38 contains therein CaFe and other materials having relatively high electrical conductivities, and the carbon electrodes 35 are sufficiently close to each other with respect to the voltage supplied thereto, the arcs are maintained and the powdered flux 38 is gradually melted by the heat of the arcs. Thus, a molten slag bath is formed in the upwardly opening portion of the metal mould M. In this case, the motor 16 is set in motion to rotate the disc slowly in one or the other direction and thereby to rotate the carbon electrodes 35 bodily in one or the other direction about the centre of the metal mould M. Hence melting of the powdered flux 38 is further promoted and the molten slag bath can be formed more quickly.

After the molten slag bath has thus been formed in the metal mould M, the circuit of the power source means 11 is opened and the carbon electrodes 35 are removed promptly from the metallic electrodes 18 respectively, following which the metal mould M and start piece 10 are elevated slightly to a position in which the lower ends of the respective metallic electrodes 18 are dipped in the molten slag bath. Then, the circuit of the power source means 11 is closed again and the electroslag re-melting of the metallic electrodes 18 is carried out while the metallic electrodes are bodily rotated about the metal mould by the motor 16, to form a molten metal pool in the metal mould. The molten metal is continuously cooled by the metal mould M to give the desired metallic product as in the conventional methods.

It is to be noted that, by using the star-connected three-phase AC. power source 11 as a power source and connecting a number, which is a multiple of 3, of metallic electrodes 18 with the carbon electrodes 35 and start piece 10 in the manner shown in FIG. 3, generation of arcs across the adjacent carbon electrodes becomes easy and the powdered flux 38 in the form of molten slag only is present between the adjacent carbon electrodes 35, which provides for conduction of current not by the arcs but by the resistance in the molten slag, so that temperature of the molten slag can be elevated to a desired level. This is the case, not only in the formation of molten slag but also in the melting of metallic electrodes 18, and is advantageous in increasing the melting efficiency of the metallic electrodes 18 with the same power of power source, particularly when the product desired to be obtained has a large cross-section.

Although the method of the invention has been described and illustrated herein as applied to an apparatus in which a metallic product is formed by re-melting metallic electrodes in a metal mould by electroslag melting while elevating the metal mould, it will be understood that the method may similarly be applied to an apparatus of the type in which a metal mould is held stationary and a metallic product is obtained by drawing a molten metal downwardly from the stationary metal mould. It should also be understood that many changes may be made to the means by which the carbon electrodes 35 are connected to the lower ends of the metallic electrodes 18, and the position and angle of the carbon electrodes.

I claim:

1. A method of forming a bath of molten slag for use in the production of metallic articles by an electroslag melting process, which method comprises:

connecting non-consumable electrodes to the lower ends of consumable metallic electrodes to be melted in the electroslag melting process;

filling a mould to be used in the electroslag melting process with flux so that the lower ends, at least, of the non-consumable electrodes, are below the level of the flux; passing an electric current between adjacent ones of the non-consumable electrodes, whereby the flux is melted to form the bath of molten slag;

removing the non-consumable electrodes from the consumable metallic electrodes prior to the melting of the consumable metallic electrodes.

2. The method of claim 1, wherein the connecting step is constituted by connecting carbon electrodes to the metallic consumable electrodes.

3. The method of claim 1, wherein, during the melting of the flux, the non-consumable electrodes are rotated bodily relative to the mould to stir the melting flux and thereby promote the formation of the bath of molten slag.

4. A process for producing metallic articles having desired cross-section configuration by continuously electroslag-remelting metallic raw materials within a mould and then cooling and solidifying said molten metal by means of said mould, characterized by the steps of connecting non-consumable electrodes to the lower ends of said metallic raw materials to be electroslag-remelted which form consumable electrodes, feeding flux into said mould to such extent that the lower ends of said non-consumable electrodes inserted into said mould to be used in the electroslag-remelting process may be embedded by said flux, passing an electric current between adjacent ones of the non-consumable electrodes to melt the flux for forming a bath of molten slag, and then removing said non-consumalbe electrodes from said consumable electrodes prior to the melting of the consumable electrodes. 

1. A method of forming a bath of molten slag for use in the production of metallic articles by an electroslag melting process, which method comprises: connecting non-consumable electrodes to the lower ends of consumable metallic electrodes to be melted in the electroslag melting process; filling a mould to be used in the electroslag melting process with flux so that the lower ends, at least, of the noncOnsumable electrodes, are below the level of the flux; passing an electric current between adjacent ones of the nonconsumable electrodes, whereby the flux is melted to form the bath of molten slag; removing the non-consumable electrodes from the consumable metallic electrodes prior to the melting of the consumable metallic electrodes.
 2. The method of claim 1, wherein the connecting step is constituted by connecting carbon electrodes to the metallic consumable electrodes.
 3. The method of claim 1, wherein, during the melting of the flux, the non-consumable electrodes are rotated bodily relative to the mould to stir the melting flux and thereby promote the formation of the bath of molten slag.
 4. A process for producing metallic articles having desired cross-section configuration by continuously electroslag-remelting metallic raw materials within a mould and then cooling and solidifying said molten metal by means of said mould, characterized by the steps of connecting non-consumable electrodes to the lower ends of said metallic raw materials to be electroslag-remelted which form consumable electrodes, feeding flux into said mould to such extent that the lower ends of said non-consumable electrodes inserted into said mould to be used in the electroslag-remelting process may be embedded by said flux, passing an electric current between adjacent ones of the non-consumable electrodes to melt the flux for forming a bath of molten slag, and then removing said non-consumalbe electrodes from said consumable electrodes prior to the melting of the consumable electrodes. 